Research Topics

Organic Batteries

Organic electrode materials are promising candidates for next-generation batteries. They consist of widely available elements, can be synthesized in processes associated with a low CO2 footprint, and are of low toxicity of even non-toxic. The diversity of organic synthetic transformations and molecular design allows making redox-active molecules with tailored properties. Through their diverse redox chemistry they can be employed in a variety of battery cell configurations, including such using multivalent metals or all-organic batteries.

In our research we focus on the development of redox-active organic materials and on their evaluation for reversible charge storage as positive or negative electrode materials in a variety of battery configurations.

 

Selected review articles by the group:

  • B. Esser, F. Dolhem, M. Becuwe, P. Poizot, A. Vlad, D. Brandell, "A perspective on organic electrode materials and technologies for next generation batteries," J. Power Sources. 2021, 482, 228814. DOI: 10.1016/j.jpowsour.2020.228814
  • B. Esser, "Redox polymers as electrode-active materials for batteries," Org. Mater. 2019, 1, 63–70. DOI: 10.1055/s-0039-3401016

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Conjugated Nanohoops

Conjugated nanohoops are intriguing compounds due to their rigid shape, cyclic conjugation and the bending of their π-system. We investigate the effects of incorporating antiaromatic panels into conjugated nanohoops and have focused on dibenzo[a,e]pentalenes (DBPs). DBP-based hoops show ambipolar electrochemical behavior and changed (anti)aromaticity compared to planar DBPs. They are chiral and can be obtained stereoselectively from chiral diketone precursors.

Selected review articles by the group:

  • B. Esser, J. S. Wössner, M. Hermann, "Conjugated Nanohoops with Dibenzo[a,e]pentalenes as Non-alternant and Antiaromatic π-Systems," Synlett 2022, 33, 737–753. DOI: 10.1055/a-1740-7139
  • M. Hermann, D. Wassy, B. Esser, "Conjugated Nanohoops Incorporating Donor‐, Acceptor‐, Hetero‐ or Polycyclic Aromatics," Angew. Chem. Int. Ed. 2021, 60, 15743–15766. DOI: 10.1002/anie.202007024

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Supramolecular Chemistry

We explore the binding between electron-rich and planar donor molecules, for example cyclic trinuclear Au(I) complexes, and acceptors with potential interest for sensing applications, as well as the incorporation of guest molecules in macrocycles, such as calixarenes and conjugated nanohoops.

 

Selected articles by the group:

  • M. Schmidt, M. Hermann, F. Otteny, B. Esser, "Calix[n]phenothiazines: Optoelectronic and Structural Properties and Host–Guest Chemistry," Org. Mater. 2020, 2, 235-239. DOI: 10.1055/s-0040-1714295
  • R. Hahn, F. Bohle, W. Fang, A. Walther, S. Grimme, B. Esser, "Raising the Bar in Aromatic Donor-Acceptor Interactions with Cyclic Trinuclear Gold(I) Complexes as Strong π-Donors," J. Am. Chem. Soc. 2018, 140, 17932–17944. DOI: 10.1021/jacs.8b08823
  • R. Hahn, F. Bohle, S. Kotte, T. J. Keller, S.-S. Jester, A. Hansen, S. Grimme, B. Esser, "Donor-acceptor interactions between cyclic trinuclear pyridinate gold(I)-complexes and electron-poor guests: Nature and energetics of guest-binding and templating on graphite," Chem. Sci. 2018, 9, 3477–3483. DOI: 10.1039/C7SC05355J

Photoredox Catalysis

In photoredox catalysis, the photo-induced electron transfer (PET) from the catalyst to the substrate is one of the most important steps. The efficiency of the PET is limited by the diffusional collision of the catalyst in its excited state and the substrate. By attaching a photoredox catalyst to a cavity that can reversibly bind the substrate, we could increase the efficiency of the PET significantly and shorten the reaction time. This concept is under further investigation in our group.

 

Proof-of-concept paper by the group:

  • M. Schmidt, B. Esser, "Cavity-promotion by pillar[5]arenes expedites organic photoredox-catalysed reductive dehalogenations," Chem. Commun. 2021, 57, 9582–9585. DOI: 10.1039/D1CC03221F

Small Molecule Semiconductors and Emitters

We investigate novel materials and concepts for small molecule organic semiconductors and emitters. Using dibenzopentalenes, we modulate their orbital energies and crystal packing by structural engineering to make them attractive ambipolar materials for n- and p-type organic field-effect transistors. For donor-acceptor-type emitters, we explored the effect of spiroconjugation on the optical properties of the compounds by incorporating spiro centers within the donor, acceptor or in between donor and acceptor unit.

 

Selected articles by the group:

  • M. Hermann, R. Wu, D. C. Grenz, D. Kratzert, H. Li, B. Esser, "Thioether- and sulfone-functionalized dibenzopentalenes as n‑channel semiconductors for organic field-effect transistors," J. Mater. Chem. C 2018, 6, 5420–5426. DOI: 10.1039/C8TC00970H
  • D. C. Grenz, D. Rose, J. S. Wössner, J. Wilbuer, F. Adler, M. Hermann, C.-Y. Chan, C. Adachi, B. Esser, "Spiroconjugated Tetraaminospirenes as Donors in Color-tunable Charge-transfer Emitters with Donor-acceptor Structure," Chem. Eur. J. 2021, 28, e202104150. DOI: 10.1002/chem.202104150
  • J. S. Wössner D. C. Grenz, D. Kratzert, B. Esser, "Tuning the optical properties of spiro-centered charge-transfer dyes by extending the donor or acceptor part," Org. Chem. Front. 2019, 6, 3649–3656. DOI: 10.1039/C9QO01134J